Influence of winding layout and airgap length on radial forces in large synchronous hydrogenerators

This paper investigates the flux density and radial force spatial harmonics in large salient pole synchronous hydro-generators. Vibration due to magnetic forces are mainly caused by low order harmonics in the airgap flux density distribution. The influence of winding layout and airgap length on the lowest order radial force component are analysed. Airgap flux density and radial force density distributions of three different generators are computed using finite element calculations. The flux density components that contributes to the lowest order force component, and the source for these harmonic components, are investigated. It is found that reducing the airgap length leads to a less than proportional increase in the lowest order radial force component. A rearrangement of the winding layout is found to be an effective method for reducing the lowest order radial force component.